CME Electrical Systems Design & Installation 2

Question 1

When sizing a feeder for a 480V, 3-phase motor load totaling 200A, what minimum ampacity must the feeder conductors have per NEC 215.2?

Accepted Answer

250A

Answer

NEC 215.2 requires feeders supplying motor loads to be sized at 125% of the largest motor's FLC plus 100% of all other loads, often resulting in 125% of total current.

Question 2

A commercial building requires a 400A, 208Y/120V, 3-phase service. Per NEC 230.79, what is the minimum service entrance conductor ampacity required?

Accepted Answer

400A

Answer

NEC 230.79(D) requires service entrance conductors to have an ampacity not less than the load to be served, so 400A service requires minimum 400A conductors.

Question 3

In a high-rise building, a 277V fluorescent lighting branch circuit serves continuous loads. What is the maximum load allowed on a 20A breaker per NEC 210.20?

Accepted Answer

16A

Answer

NEC 210.20(A) limits continuous loads on a branch circuit to 80% of the overcurrent device rating, so a 20A breaker allows maximum 16A continuous load.

Question 4

What NEC table is used to determine the maximum number of current-carrying conductors permitted in a conduit before derating is required?

Accepted Answer

Table 310.15(B)(3)(a)

Answer

NEC Table 310.15(B)(3)(a) provides adjustment factors for more than three current-carrying conductors in a raceway, requiring derating when exceeded.

Question 5

A 3-phase, 480V system has an available fault current of 65,000A at the service entrance. What must all downstream equipment be rated for?

Accepted Answer

At least equal to the available fault current

Answer

NEC 110.9 and 110.10 require all equipment to have an interrupting rating sufficient for the available fault current at the point of installation.

(CME) Certified Master Electrician Practice Test

(CME) Certified Master Electrician Practice Test

CME Electrical Systems Design & Installation 2